As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for batteries has also sharply increased as an energy source for the mobile devices. Also, much research on batteries satisfying various needs has been carried out.
In terms of the shape of batteries, the demand for prismatic secondary batteries or pouch-shaped secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for batteries, the demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, having high energy density, high discharge voltage, and high output stability, is very high.
Furthermore, secondary batteries may be classified based on the construction of an electrode assembly having a cathode/separator/anode structure. For example, the electrode assembly may be constructed in a jelly-roll (winding) type structure in which long-sheet type cathodes and anodes are wound while separators are disposed respectively between the cathodes and the anodes, a stacking type structure in which pluralities of cathodes and anodes having a predetermined size are successively stacked while separators are disposed respectively between the cathodes and the anodes, or a stacking/folding type structure in which pluralities of cathodes and anodes having a predetermined size are successively stacked while separators are disposed respectively between the cathodes and the anodes to constitute a bi-cell or a full-cell, and then the bi-cell or the full-cell is wound.
Recently, much interest has been taken in a pouch-shaped battery constructed in a structure in which such a stacking or stacking/folding type electrode assembly is mounted in a pouch-shaped battery case made of an aluminum laminate sheet because of low manufacturing costs, light weight, and easy modification in shape. As a result, the use of the pouch-shaped battery has gradually increased.
FIG. 1 is an exploded perspective view typically illustrating the general structure of a conventional representative pouch-shaped secondary battery.
Referring to FIG. 1, the pouch-shaped secondary battery 10 includes an electrode assembly 30, pluralities of electrode tabs 40 and 50 extending from the electrode assembly 30, electrode leads 60 and 70 welded to the electrode tabs 40 and 50, respectively, and a battery case 20 for receiving the electrode assembly 30.
The electrode assembly 30 is a power generating element comprising cathodes and anodes successively stacked while separators are disposed respectively between the cathodes and the anodes. The electrode assembly 30 is constructed in a stacking structure or a stacking/folding structure. The electrode tabs 40 and 50 extend from corresponding electrode plates of the electrode assembly 30. The electrode leads 60 and 70 are electrically connected to the electrode tabs 40 and 50 extending from the corresponding electrode plates of the electrode assembly 30, respectively, for example, by welding. The electrode leads 60 and 70 are partially exposed to the outside of the battery case 20. To the upper and lower surfaces of the electrode leads 60 and 70 are partially attached insulative films 80 for improving sealability between the battery case 20 and the electrode leads 60 and 70 and, at the same time, for securing electrical insulation between the battery case 20 and the electrode leads 60 and 70.
The battery case 20 is made of an aluminum laminate sheet. The battery case 20 has a space defined therein for receiving the electrode assembly 30. The battery case 20 is formed generally in the shape of a pouch. In the case that the electrode assembly 30 is a stacking type electrode assembly as shown in FIG. 1, the inner upper end of the battery case 20 is spaced apart from the electrode assembly 30 such that the plurality of cathode tabs 40 and the plurality of anode tabs 50 can be coupled to the electrode leads 60 and 70, respectively.
When the pouch-shaped battery is overcharged, exposed to high temperature, or short-circuited, a large amount of gas is generated due to the decomposition of an electrolyte, with the result that the battery case swells, i.e., a so-called swelling phenomenon occurs. This swelling phenomenon accelerates the decomposition of the electrolyte, while inducing high pressure in the sealed battery case, thereby inducing the explosion of the battery. Furthermore, the central portion of the battery case swells due to the generated gas, and therefore, the battery is deformed. As a result, a short circuit occurs in the battery.
In order to solve this problem, there have been proposed several methods of forming a predetermined non-sealing portion between an electrode assembly and a sealing portion of a battery case. For example, Japanese Patent Application Publication No. 2005-332726 and No. 2005-222872 disclose secondary batteries each having an stacking type electrode assembly mounted in a receiving part of a laminate sheet, each secondary battery being constructed in a structure in which a non-sealing portion is formed between the receiving part of the laminate sheet, in which the electrode assembly is mounted, and a sealing portion of the laminate sheet, such that the sealing portion, which is welded at one side of the laminate sheet, is widened, in an abnormal operating condition of the secondary battery, for example, when the secondary battery is overcharged or the interior temperature of the secondary battery is greatly increased, with the result that gas is discharged out of the secondary battery.
Specifically, Japanese Patent Application Publication No. 2005-332726 discloses a structure in which a space having a predetermined width is formed inside the receiving part of the laminate sheet, in which the electrode assembly is mounted, along the outer circumference of the receiving part. As a result, the size of the receiving part is large as compared to the size of the electrode assembly. Consequently, it is difficult to correctly position of the electrode assembly in the receiving part, such that the space is formed inside the receiving part, in a practical manufacturing process. Furthermore, it is difficult to construct the secondary battery such that sealed gas discharge region is reliably widened when high pressure is generated in the secondary battery.
Also, Japanese Patent Application Publication No. 2005-222872 discloses a structure in which a gas channel, for allowing a gas discharge region to be reliably widened, is mounted in a laminate battery case, and a gas channel guide member is made of a material having a higher strength than that of the laminate sheet. Consequently, the manufacturing process is complicated, and manufacturing costs are high, with the result that the disclosed structure is limited to be applied to a practical manufacturing process.
Consequently, there is a high necessity for a technology to fundamentally solve the above-mentioned problems.